The present invention relates generally to the bell end of a plastic pipe joint and more particularly to a bell end designed for use in pressure service and to a method of making the bell end.
There are presently a number of conventional ways to manufacture the bell end of a bell and spigot joint from one end section of a plastic pipe, specifically a polyvinyl chloride (PVC) plastic pipe. In one such method, the end section of the pipe is first heated to its state of thermal deformability. While in this state, the heated end section is moved along and around a flared or bell shaped mandrel. In some cases, for example in U.S. Pat. Nos. 3,793,427; 3,807,027 and 3,924,999, an annular sealing gasket is positioned around the mandrel prior to forming the heated end section around the latter. In this way, a circumferential groove is formed in the bell end for housing the sealing gasket.
Where the bell end just described is formed from an end section which is initially the same thickness as the rest of the pipe, the wall defining the resultant bell end will of course be thinner. This is perfectly satisfactory where the pipe joint including such a bell end is intended for use in nonpressure service. However, where the pipe joint is intended for use in pressure service, some specifications require that the wall defining the bell end be thicker in cross-sectional configuration than would be the case by belling the normal configuration of the pipe. One way to accomplish this is by thickening the end section of the pipe to be belled before belling takes place. This can be carried out during the actual extrusion of the pipe, as described in U.S. Pat. No. 3,264,383, or it can be carried out after formation of the pipe, as described in copending U.S. application Ser. No. 722,187, filed Sept. 17, 1976.
As will be discussed in more detail hereinafter, the present invention is also directed to a pipe joint and particularly to a bell end intended for use in pressure service. However, the bell end constructed in accordance with the present invention is neither pre-thickened nor post-thickened but rather utilizes a rather unique combination of components to make it suitable for pressure service.